Question detail
Outline the mechanism of electrophilic substitution in benzene when it reacts with bromine in the presence of a catalyst.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Aromatic chemistry (A-level only)
Question
Outline the mechanism of electrophilic substitution in benzene when it reacts with bromine in the presence of a catalyst.
Answer
The electrophilic substitution mechanism involves the generation of a bromonium ion from bromine, which acts as the electrophile. The benzene ring donates a pair of electrons to form a bond with the bromonium ion, creating a sigma complex. This complex then loses a proton to regenerate the aromatic system, resulting in bromobenzene.
Explanation
This answer is strong because it clearly describes the steps involved in the electrophilic substitution mechanism, highlighting the role of the electrophile and the regeneration of the aromatic system. The question tests the student's understanding of the reaction mechanism specific to benzene.
Common mistake
Incorrect intermediate: benzyl cation
Students think the electrophilic substitution proceeds via a benzyl carbocation intermediate that retains aromaticity.
The correct intermediate is a σ‑complex (arenium ion) where the aromatic π system is temporarily disrupted; aromaticity is restored after deprotonation.
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